A common type of membrane switch assembly comprises a substrate, a flexible membrane, and a separator positioned between the membrane and the substrate. Switch electrodes are provided on the opposed surfaces of the membrane and the substrate and circuit conductors extend between and among the electrodes on at least one of the surfaces. A tail extends from the assembly and the lead portions of selected circuit conductors extend onto the tail. The lead portions on the tail are, in turn, connected to external conductors. It is common practice to provide the tail as an extension of the membrane or, if the substrate is also of flexible material, as an extension of the substrate.
The circuit designer frequently encounters problems in the design of membrane switches of the type described above in that he encounters difficulty in laying out the circuit conductors such that lead portions can be provided on the tail. If circuit conductors are provided on both the membrane surface and the substrate surface, he must then extend circuit conductors across the fold line (if the switch assembly is a folded sheet of film) to the member having the tail extending therefrom. Quite often, the circuit designer will provide all of the circuit conductors on the membrane and have only commoning conductors on the substrate in order to avoid the necessity of having long circuit conductors extending across the fold line. This expedient, however, is often impractical because of the complexity of the circuit and it is necessary to provide circuit conductors on both the membrane and the substrate.
The present invention is directed to the achievement of an improved membrane switch assembly which will greatly simplify the task of the circuit designer in laying out the circuit conductors and providing lead portions on the tail of the switch assembly. The invention is thus directed to the achievement of an improved membrane switch assembly which permits a reduction in the complexity of the circuit and economies in the manufacture of the switch assembly.
A membrane switch assembly in accordance with the invention comprises a substrate, a membrane which is of a flexible insulating material, and a spacer layer between the membrane and the substrate. The substrate and the membrane have opposed first and second surfaces respectively, the opposed surfaces having opposed switch electrodes thereon at switch sites. The spacer has openings therein at the switch sites. Circuit conductors extend between and among the switch sites, and a tail extends from the assembly. The circuit conductors have leads which extend into the tail. The membrane switch assembly is characterized in that the substrate is also of a flexible insulating material and the tail comprises a substrate tail section, which extends from the substrate, and a membrane tail section which extends from the membrane. The tail sections are in parallel planes, are substantially co-extensive, and have opposed first and second tail surfaces which are contiguous with the opposed first and second surfaces of the substrate and the membrane respectively. The substrate and the membrane each have circuit conductors thereon, the circuit conductors on the substrate having substrate leads which extend onto the first tail surface and the circuit conductors on the membrane having membrane leads which extend onto the second tail surface. The substrate leads extend parallel to the membrane leads and are offset with respect to the membrane leads.
The substrate tail section and the membrane tail section each has a free end and side edges extending to the free end. Each tail section further has an end portion which extends to the free end from a location adjacent to its free end. The substrate leads and the membrane leads extend to the free end of the substrate tail section and the membrane tail section respectively and have contact portions extending across the end portions of the substrate tail section and the membrane tail section, the contact portions being exposed with the contact portions of the substrate leads facing oppositely with respect to the contact portions of the membrane leads.
The membrane tail section and the substrate tail section each have at least one slot extending transversely of the side edges of the tail sections, the slots being spaced from the free ends of the tail sections. A part of the end portion of the substrate tail section extends through the slot in the membrane tail section and a part of the end portion of the membrane tail section extends through the slot in the substrate tail section, the parts of the end portions which extend through the slots having the contact portions of conductors thereon.
A further embodiment is characterized in that the substrate leads are grouped on one side of a medial axis which extends from the free end of the tail between, and is parallel to, the side edges of the tail. The membrane leads are on the other side of the medial axis. The slot in the substrate tail section is on the other side of the medial axis and the slot in the membrane tail section is on the one side of the medial axis. An alternative embodiment is characterized in that the substrate leads are on both sides of the medial axis and the membrane leads are also on both sides of the medial axis, the slots in the substrate tail section and in the membrane tail section being in alignment with the membrane leads and the substrate leads respectively. The substrate tail section and the membrane tail section each have slits extending from their free ends inwardly through the end portions thereof, the slits forming flaps which are inserted through the slots.